That's correct, they served under Emperor Ronan Fel .Around 137 ABY. The Sith attacked the Empire and the Empire split in a power struggle between the true Emperor (Ronan Fel) and the Sith. This was the Legacy series "Broken" from the Dark Horse Comics.

Sometimes it fun just to make a costume and wear it at conventions, I have a few that are not 501st or RL, like my Biggs Darklighter Legacy TIE Pilot. I must have to agree with Thomas on this one, tho the costume is awesome looking and I would love to make it and wear it, this is a RL costume and not a 501st.